UV Weathering and Related Test Methods - Cabot Corporation

6
Light stabilizers for plastic materials
To provide an appropriate protection against UV radiation, several stabilizing systems can be utilized in plastic materials.
The most important types of light stabilizers are Ultraviolet Light Absorbers, Energy Transfer Agents or Quenchers, as
well as Hindered Amine Light Stabilizers. A brief description of these different light stabilizers is given below.
a) UV light absorbers
Absorbers convert harmful ultraviolet radiation to harmless infrared
radiation or thermal energy, which is dissipated through the polymer
matrix. They can be either transparent as hydroxybenzophenone or
opaque like carbon black.
Carbon black
Carbon black is one the most efficient and widespread light
absorbers. Its efficiency as a UV absorber depends primarily on the
primary particle size and structure. At the same loading, carbon black
aggregates based on fine prime particles will present more surface to
incident light - and hence a larger ultraviolet light absorbing efficiency
- than a coarser grade.
Primary particle
Carbon black aggregate
Primary particle size
(typically 15 to 60 nanometers)
Effect of primary particle size on weathering performance
%RE at break
125
100
75
50
25
0
Accelerated Weathering – ATLAS
55 µm LDPE films with 2.5% CB
0 250 500 750 1000 1250
Exposure time (hours)
The appropriate loading level depends on the part thickness, exposure
conditions and type of carbon black. Usual loadings to impart
optimum UV protection vary between 2 and 3% (it should be noted
that these carbon black levels correspond to 4 to 7% masterbatch,
depending on their loading).
< 25 nm particle size
60 nm particle size